The present invention pertains to a singulation apparatus for preforms with a device for eliminating mispositioned preforms. Such singulation apparatuses are required in the technical area of the conveyance of preforms to a machine for the production of containers from a thermoplastic material, wherein the containers are formed by the action of blowing pressure.
In the process of forming containers by the action of blowing pressure, preforms of a thermoplastic material such as preforms of PET (polyethylene terephthalate) are sent to various processing stations within a blow-molding machine. A blow-molding machine of this type typically comprises a heating device and a blowing device, in the area of which the previously tempered preform is expanded into a container by biaxial orientation. The expansion occurs by means of compressed air, which is introduced into the preform to be expanded. The course of the processing technology involved in a preform expansion of this type is explained in DE-OS 43 40 291. The basic configuration of a blow-molding station for forming containers is described in DE-OS 42 12 583. Possibilities for tempering the preforms are explained in DE-OS 23 52 926. Reference is made to the content of these documents.
The blow-molding machine must be supplied continuously with preforms so that the feed to the blow-molding machine will not be interrupted. This is true both for linear blow-molding machines and for those based on the rotary wheel principle. There are two alternative ways in which the preforms can be sent to the blow-molding machine. In the case of the so-called “one-step” method, the preforms are produced by an injection-molding process, and, immediately after they have been injection-molded (and after they have solidified sufficiently), they are transported directly to the blow-molding machine by a conveying apparatus. In the case of the so-called “two-step” method, the preforms are first produced by an injection-molding process and then stored; they are conditioned with respect to their temperature and then blown into containers only at a later time. The production of the preforms and the blow-molding of the preforms into containers can take place at different times and at different places.
Both methods have in common that the preforms are sent to the blow-molding machine by a conveying apparatus. Known apparatuses consist of, for example, a vertical conveyor, by which the preforms, which are stored in a collecting bin, are transported to a conveying device. By means of the conveying device, usually a conveyor belt, the preforms are transported to a singulation apparatus. This singulation apparatus has the task of orienting the preforms so that assume a defined position and of singulating them so that they can be transferred properly to, for example, a downstream blow-molding machine. Known singulation apparatuses (so-called “roll sorters”) consist of, for example, two conveying rolls, which rotate around their axes in opposite directions and between which a narrow gap remains, which is selected so that the preforms can be held, suspended by their collars, between the rotating conveying rolls. The rotational axes of the conveying rolls are arranged parallel to each other, so that the two axes define a plane. The conveying rolls are arranged with a gradient, that is, at a certain angle to the horizontal, so that the preforms slide along the conveying rolls in the direction of the gradient. In this way, the preforms are sorted in suspended fashion, singulated between the rotating rolls, and also conveyed as a result of the gradient. The conveyance of the preforms in the singulation apparatus occurs in a conveying plane, which is parallel to the plane defined by the two rotational axes of the conveying rolls, so that the conveying plane also comprises the above-mentioned angle to the horizontal.
It is known that preforms which have not been properly sorted and therefore project above a predefined height, for example, can be sorted out. Such sorting-out devices are known from, for example, WO 2011/069268 A1. There the sorting-out is realized by the action of a blast of air. In this document, additional sorting-out devices according to the prior art are also discussed.
It is also known that rotating wheels can be used to accomplish the sorting-out task; these are also called “kicker wheels”. Kicker wheels are known which are arranged to work in a backflow manner. The rotational axis of such wheels is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rolls of the roll sorter. The rotational direction is selected so that the rotating paddles of the wheel move in the direction opposite to that in which the preforms are being conveyed. A preform which projects above the predefined height is gripped by a paddle of the paddle wheel, pulled out in the direction opposite the conveying direction and opposite the oncoming preforms, and ejected. It is considered a disadvantage that this results in the creation of large gaps in the flow of performs.
An alternative configuration is described in DE 601 18 772 T2, which shows a kicker wheel arranged above the conveying rolls of a roll sorter. In a first example, the rotational axis of the kicker wheel is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rolls of the roll sorter, wherein the rotational axis is at an angle to its conveying direction. When a preform is gripped, the angled position has the effect of ejecting the preform both to the side and in the backflow direction simultaneously. It is still considered a disadvantage, however, that in this way gaps are formed in the flow of preforms.
In the second example described in DE 601 18 772 T2, the rotational axis of the kicker wheel is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rolls of the roll sorter, wherein the rotational axis is now parallel to the conveying direction. When a preform is gripped, only a sideways-acting ejection force is applied. In this configuration, it is considered disadvantageous that the paddles of the kicker wheel can dip to only a small degree between the conveying rolls and that it is impossible to adjust the height of the wheel.